1. Field of the Invention
This invention relates to the cooling of electrical induction furnaces and more particularly it concerns novel methods and apparatus for providing emergency cooling to such furnaces.
2. Description of the Prior Art
It is known to cool electrical induction furnaces by flowing a primary coolant liquid, such as water, through coils in or around the furnace and then to pass the coolant liquid through a primary heat exchanger for example, an evaporation cooling tower. Cooling systems such as this are shown and described in a publication entitled Water Systems and Water Treatment for Coreless Induction Furnaces, published in 1977 as a report of Committee 8C of the American Foundrymen's Society, Incorporated, Des Plaines, Ill.
As further pointed out in the above mentioned publication, the primary coolant liquid is specially treated, for example, demineralized, in order to minimize corrosion and scale buildup in the various coils and passageways through which it flows. In some instances an additive, such as glycol, is provided to avoid freezing when the furnace is shut down during cold weather. These treatments are relatively expensive. Accordingly, in order to maintain the treated condition of the treated coolant liquid, and to avoid the necessity to add substantial amounts of additional liquid, the flow path for the primary coolant liquid is in the form of a closed circuit and the external primary heat exchanger employs indirect heat exchange, that is, the heat from the coolant liquid passes through tube walls to another fluid which does not directly contact the coolant liquid. A recirculating pump is provided along the closed circuit and pumps the primary coolant liquid so that the same liquid recirculates through the furnace, through the indirect primary heat exchanger and back around through the furnace again.
It is necessary to provide an emergency cooling arrangement to prevent overheating of the furnace in the event of a breakdown in the recirculating pump or in the heat exchanger. In the past, the emergency cooling arrangement comprised means to supply an emergency coolant liquid to the system. Usually there was provided an emergency coolant line converted to a municipal water supply which served as a source of emergency coolant liquid. When a breakdown occurred a valve was opened in the emergency coolant line and municipal water was forced by its own pressure into and through the furnace coils; and the emergency coolant liquid, i.e. the municipal water, would force the primary coolant ahead of it and out through a drain.
The emergency cooling system of the prior art was simple and convenient; however it had two disadvantages. Firstly, it resulted in a loss of the primary coolant liquid, which is expensive. Secondly, it also resulted in the furnace cooling system being charged with untreated water, which increased the potential for corrosion and scale buildup.